To the point -- is it possible that my dirted tank is cycling itself without any added ammonia, fish, or anything? I have not read about such scenarios, and I only have about 1 inch of MGOPS capped by black diamond blasting sand (not that much dirt), and I think whatever the dirt is leaching out has gotten me past the Ammonia phase into the Nitrite phase -- excuse the semantics here if i'm saying it wrong... Basically my API test had ammonia's around the 3ppm level for a few days with zero nitrites. Ammonia's are now down to about .25ppm, and my nitrites are up to 4ppm.

Is it possible that this is a fishless cycle of sorts without adding anything to the tank?

Some other details that might be important -- the dirt/sand has been in the tank for about 3 weeks, but I had been doing heavy water changes at first to clear up the water which was kind of stirred up. I now haven't done any water changes since last sunday, so it makes sense that in the last week or so i've seen ammonia and nitrite finally spike.

As for next steps, I have two large bottles of Tetra SafeStart coming in the mail -- I don't need to use it but figured it's not bad to have. If I see the nitrites come down (and ammonia stay down) should I get a few hardy fish such as giant danios and put them in the tank with the TSS? Point being whatever good bacteria I've grown would be kept alive and fed.

I'm not trying to be irresponsible and add fish early or anything, but that actually seems kind of logical. I apologize for all of the questions, I've never done a dirted tank before, so this is a new variable that i'm not used to accounting for. 

(Bonus question -- how long does MGOPS leach ammonia for?)